The present invention relates to sensor testing apparatus and, more particularly, to a fiber optic sensor testing apparatus that produces optical energy of any polarization state to effect sensor testing and evaluation.
Polarization sensitive single-mode fiber optic sensors modulate polarized optical energy to produce a measured signal change. These sensors are used in a wide variety of applications, and, as such, a need exists to test and calibrate these devices to ensure their continued operating accuracy. Since the sensors can be designed to modulate or otherwise affect a particular type of polarized optical energy, it is desirable to construct a sensor testing apparatus that will provide any type or state of polarized optical energy so that any sensor may be tested. The testing apparatus must detect the polarization state of the optical energy it generates and supplies to the sensor under test as well as the polarization state of the optical energy exiting the sensor and provide a meaningful measure of the modulation effect of the sensor upon the source light provided by the testing apparatus.
One of the problems associated with conventional polarimeters is that they are limited in the types of polarization states they provide for test purposes and do not provide optical energy in all polarization states. For example, U.S. Pat. No. 2,976,764 to Hyde et al. presents a polarimeter that transmits only linearly or elliptically polarized optical energy, and U.S. Pat. No. 3,741,661 to Yamamoto et al. transmits only circularly polarized optical energy. Accordingly, these polarimeters are limited to testing sensors which are sensitive to optical energy of the particular polarization state offered by the device.
A drawback associated with conventional testing apparatus is that they require multiple measurements to determine the polarization state of the optical energy transmitted from the sensor thereby lengthening the testing and calibration sequence.